This invention relates to electrophotographic copying apparatus, and more particularly it is concerned with an electrophotographic copying apparatus capable of forming a plurality of sizes of images on the image forming surface of a photosensitive member.
In many types of electrophotographic copying apparatus, copying of a document can be performed in a plurality of sizes of images, and different sizes of images can be formed on the image forming surface of the photosensitive member. In electrophotographic copying apparatus of the prior art, it has hitherto been usual practice to start forming images from the same position irrespective of the sizes of the images formed. Thus when it is desired to form three different sizes of images or an image of A4 size (210 mm.times.297 mm), an image of B4 size (257 mm.times.364 mm) and an image of A3 size (297 mm.times.420 mm), for example, on the image forming surface of a photosensitive member having a size large enough to form two image segments of the A3 size, the number of image segments that could be formed on the entire area of the photosensitive member would be limited to two of any size or sizes.
Market researches have shown that even if an electrophotographic copying apparatus capable of producing copies of a large size, such as A3 size, is used, the majority of copying operations performed in offices and factories by using such apparatus are intended to produce copies of smaller sizes, such as A4 size, in actual practice.
When the photosensitive member is used in the manner described hereinabove, the major portion of the image forming surface of the photosensitive member would be wasted because only a small portion is actually used but also different portions of the image forming surface of the photosensitive member would show different degrees of fatigue because a portion of a certain length from the image forming starting position is used at all times, and damage caused to the image forming surface of the photosensitive member when transfer-prining sheets are separated therefrom, for example, would be concentrated in a specific portion and the service life of the photosensitive member would be greatly reduced.